The present invention relates to apparatus and methods for rendering electric cables repellent to rodent attacks utilizing the toxic effect of the lithium ion which results when a lithium containing chemical such as the non-lethal toxic chemical agent lithium chloride, is dissolved by the saliva of the rodent.
Many rodents and in particular the fox squirrel (Sciurus niger) habitually chew on aerial communication cables. Such chewing frequently causes immediate damage to the cable's wiring or results in damage when rain water or other moisture enters the holes gnawed through the protective outer insulation. In the case of squirrels, chewing on objects which are tough in composition is necessary to prevent their ever-growing incisor teeth from overgrowing. Thus, simply providing a hard outer cable covering is insufficient and may even provide an inducement rather than a deterrent to chewing by squirrels. Because it is frequently undesirable to simply kill the rodents, it is necessary to devise non-lethal apparatus and methods whereby rodents such as squirrels will be prevented or deterred from chewing on cables.
Numerous psychological studies have been performed which show that psychological barriers can be induced by causing an undesirable effect to result immediately after an act is performed. The animal then associates the undesirable result with the immediate preceding act and thereafter changes its behavior to prevent the undesirable result. In the present invention, this knowledge is utilized to incorporate, in a cable assembly, a non-lethal but toxic chemical agent which is capable of causing rapid illness thereby inducing a psychological barrier resulting in a behavioral change opposed to the cable chewing.
The utilization of chemical agents to repel or prevent damage caused by animals either chewing or gnawing on the item sought to be protected is well known. For example, see U.S. Pat. No. 3,426,133, filed Mar. 21, 1966 by James A. Shotton, U.S. Pat. No. 3,269,902, filed Aug. 31, 1964 by Lyle D. Goodhew et al. However, neither of these patents utilize the toxicity of the lithium ion in a non-lethal, toxic chemical such as lithium chloride as an agent to repel rodent attacks on electric cables. In the present invention, however, a layer or surface coating of lithium containing chemical which produces lithium ions when dissolved in the saliva of an animal is provided in an electric cable assembly to provide such a non-lethal but toxic chemical. The lithium ion is the active or illness producing agent and operates to replace the sodium in the sodium-potassium pump of animals thus causing illness (see "Modern Drug Encyclopedia and Therapeutic Index" 13th Edition by Arthur J. Lewis, published by Yorke Medical Books, Dun-Donnelley, New York, 1975, at pages 460-461). Lithium chloride has been found particularly suitable because of the rapidity with which illness is induced upon the ingestion of a minute amount of the chemical. For example, in various experiments test animals became visibly ill within one and a half to five minutes upon the ingestion of as little of 0.3 gram of lithium chloride. The experiments showed that this short time span between ingesting the lithium chloride and becoming sick created an association between chewing on or eating an item and becoming sick. This association caused a behavioral change which later deterred the animals from eating or gnawing on the items which looked like the item onto which the lithium chloride had been applied even though such items did not later contain the lithium chloride. Thus, the present invention is capable of protecting electric cables around which the lithium chloride is placed as well as older cables not so protected but which appear the same to animals such as squirrels.